1. Field of the Invention
The present invention relates to the field of motor vehicle safety and relates more particularly to a protective assembly comprising a module itself containing a gas generator, an external deflector and an air bag.
2. Description of Related Art
In order to limit as far as possible the risk of physical injury run by the occupants of a motor vehicle in the event of a frontal or side impact, it has been proposed for the past thirty or so years that gas-generating systems be incorporated into the motor vehicles to inflate frontal or side protective air bags. However, these generators, which are becoming ever more powerful while at the same time retaining a small external size, generally emit insufficiently filtered jets of gas which come into direct contact with the air bag and convey very hot particles which may damage the air bag.
It has therefore been proposed that external deflectors be associated with these various gas generators so as to deflect the path of the gas jets and therefore reduce their aggression towards the air bags. U.S. Pat. No. 3,618,976 describes a cylindrical gas generator more especially used to inflate an air bag intended to protect the driver of a motor vehicle and which comprises a central orifice for discharging the gases which originate from the combustion of a pyrotechnic charge, this central orifice, located on a flat face of the generator, being of rectangular shape and surmounted by a non-deformable deflector, itself borne by an expanding filter, also of rectangular shape, which is riveted and initially folded around the said central orifice. An air bag is positioned over the generator and contains the non-deformable deflector. However, the latter, aside from the fact that it leads to a relatively high production cost and an excessive external size, can be used only with a gas generator of a certain type as described in the said patent and cannot therefore be associated with a generator of tubular shape equipped with peripheral gas discharge orifices. U.S. Pat. No. 5,340,147 discloses a protective assembly containing a gas generator of tubular overall shape with gas outlets distributed around the entire length of the cylindrical wall of the generator and around which a non-deformable external deflector is fixed, this deflector itself being contained in a diffuser which is partially expandible and of tubular overall shape. This protective assembly is made using many mechanical parts which are difficult to machine, thus giving the latter a high cost of manufacture and a high mass and large external size, which is highly penalizing in a competitive market such as that of motor vehicle safety. European patent application EP 0,844,149 describes a protective assembly comprising a cylindrical gas generator of short height by comparison with its diameter and used more especially to inflate an air bag intended to protect the driver of a motor vehicle. A non-deformable external deflector is placed around the generator and allows the jets of hot gases to be deflected.
The need for tubular generators which are very long by comparison with their diameter is ever growing at the present time because of the proliferation of protective devices for passengers, these devices calling exclusively upon this type of generator. Now, the person skilled in the art does not have any external deflector of small size and which is inexpensive to manufacture for this type of generator.
A first object of the invention is to produce a protective assembly containing a gas generator of tubular overall shape, with which there is associated an external deflector, the external size of which is small.
Another object of the invention is to produce a protective assembly of this type which has a low cost of manufacture.
An assembly for protecting an occupant of a motor vehicle comprises, according to the invention, a module itself containing a gas generator, an external deflector and an air bag initially folded around the said gas generator, characterized in that:
i) the gas generator comprises a body which has two ends and a side wall bearing discharge orifices distributed around the circumference of the said side wall, the latter having a circular cross section, the outside perimeter of which has a length L,
ii) the external deflector consists of a single expanding element,
iii) the discharge orifices are initially covered by the expanding external deflector which closely surrounds the side wall.
As a preference, the expanding external deflector is made using a deformable metal strip which is between 1.5 L and 2.5 L long. Also as a preference, the strip is between 0.1 mm and 0.5 mm thick.
Advantageously, the deformable strip has at least one expanding region intended to be deployed under the action of the gases released by the generator. This expanding region may be produced by folding the strip or alternatively by rolling the strip up on itself.
According to a first alternative form of the expanding external deflector, the expanding region is obtained by folding the strip in at least four symmetric folds, each fold being folded at an angle of 180xc2x0 and with a minimum radius of 0.2 mm.
According to a second alternative form of the expanding external deflector, the expanding region is obtained by folding the strip in at least two asymmetric folds, each fold being folded at an angle of 180xc2x0 and with a minimum radius of 0.2 mm.
A protective assembly as described hereinabove therefore does indeed afford a solution to the aforeset problems because:
the use of an expanding external deflector which initially closely surrounds the side wall of the generator allows the subassembly consisting of the said generator and the said deflector to be given an external size which is practically similar to that of the generator.
the use of a simple metal strip of negligible mass from which to make the expanding external deflector allows manufacturing and assembly costs to be greatly reduced.
Advantageously, the strip is coated with anti-corrosion protection.
Advantageously too, the discharge orifices are located in a region which is equidistant from the ends of the body of the generator. In order to reduce the number of stages needed in assembling the protective assembly, the gas generator, the expanding external deflector and the air bag are attached to the module using a common fastener. As a preference, the latter consists of a threaded shank fixed into the side wall of the generator and on which a nut is fitted.
One embodiment of a protective assembly according to the invention is described hereinafter in FIGS. 1 to 4, and FIGS. 5 to 8 give examples of the metal strip used to manufacture the expanding external deflector.